PROJECT SUMMARY Individuals treated for hypertension remain at elevated risk for cardiovascular disease (CVD) even when their blood pressure is treated and controlled. The reason for this is unclear. Our preliminary data suggest low vitamin K status is a risk factor for coronary artery calcium progression (indicative of subclinical CVD) in persons treated for hypertension, but not in persons not treated for hypertension. It is not known if low vitamin K status is similarly associated with incident clinical CVD in persons treated for hypertension. To fill this knowledge gap, we propose to conduct a participant-level meta-analysis to determine if the association between vitamin K status and incident clinical CVD differs in persons treated for hypertension compared to persons not treated for hypertension (including with untreated hypertension and normal blood pressure). Hypertension, arterial stiffness, and CVD are inter-related, and vitamin K-dependent mechanisms are implicated in arterial stiffness, so we will also determine if the association between vitamin K status and change in arterial stiffness over 6-8 years differs in persons treated for hypertension compared to persons not treated for hypertension (including with untreated hypertension and normal blood pressure). There are no known strategies to reduce the increased residual risk for CVD associated with hypertension treatment. Identifying vitamin K status as a risk factor for CVD in treated hypertensives could lead to a paradigm-shifting and easily-implementable approach to address an important clinical barrier associated with hypertension treatment because vitamin K is safe, inexpensive and readily available.